slender rostrum and numerous teeth of the Piatanistids and the
squared excavations of the maxillaries. Argyrocetus patagonicus
possessed also archaic characters, suggesting earlier affinities still.
The two eondyles of the skull instead of being closely adpressed
to the skull stood out in a way more like that met with in
terrestrial mammals. The nasal bones instead of being abbreviated
rudiments are well developed as in the archaic Zeuglodonts.
The cervical vertebrae of this Whale are all perfectly free from
each other and individually long. The skull is on the whole
bilaterally symmetrical; this again is a feature more pronounced
among the Platanistidae than among other Odontocetes. Accom-
panying these generalised Cetacean characters are some which
show that the animal was too specialised to be the direct ancestor
of any existing forms. The end of the mandible was upturned
and without teeth, its form, being quite unique among Cetacea.
Other allied forms, such as ^arrhaehis and PriscodelpJiinits,
showed the same length of the cervical vertebrae.
A very distinct family of extinct Whales is that of the
Squalodontidae. They to some extent bridge over the gap
between the existing Odontoceti and the Eocene Archaeoceti
The skull of these Whales was on the whole Dolphin-like.
But they possessed teeth which were distinctly specialised into
incisors, canines, and molars. The molars have a coarsely-serrated
cutting edge as in the Zeuglodonts, and are also to some extent
two-rooted. But they are more numerous, and so far approximate
to the conditions which characterise the more typical modern
Odontocetes. Sgualodon was a long-beaked form, and Prosgualodon
had a skull whose proportions are nearer those of
SUB-ORDER 3. ABCHAEOCETL
This division of the Whale tribe embraces but a single family
Eeuglodonticiae, of which but a single genus, Zeuglodon^ can with
certainty be discriminated*
Z&iLglodoii is an Eocene form of large size, with teeth whict
are limited in number and disposed in three series as incisors
canines, and molars. The molars are double-rooted, a fact whict
lias given to the genus its name. The nasal bones being lon|